ShowerAxis mixes signed and unsigned int in comparison

ShowerAxis.cc:23:13: warning: comparison of integers of different signs: 'const int' and 'std::vector::size_type' (aka 'unsigned long') [-Wsign-compare] if (upper >= X_.size()) {

created merge request !215 (merged) to address this issue

mentioned in merge request !215 (merged)

assigned to @mreininghaus

closed via merge request !215 (merged)

mentioned in commit 62a8de09